Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:    AP access point    BTS base transceiver station    CRC cyclic redundancy check    DVB digital video broadcast    FDD frequency division duplex    GPS global positioning system    GSM global system for mobile communication    IP internet protocol    MAC medium access control    O&M operations and management    PCI peripheral component interface    QAM quadrature amplitude modulation    SGMII serial gigabit media independent interface    TDD time division duplex    TDM time division multiplex    USB universal serial bus    WCDMA wideband code division multiple access    WLAN wireless local area network    WMN wireless mesh network
Meshed wireless networking is becoming an important method for backhauling traffic from radio access nodes. The field of wireless meshed networking has evolved from military use over the past several decades into commercial applications such as those found in WiFi and WiMAX systems. Current research has been directed to a single radio backhaul meshed with 360 degree omnidirectional coverage. For multi-radio systems research has primarily been directed point-to-point or point-to-multipoint systems.
As radios are becoming less expensive it is economically feasible to package multiple radios into one meshed node. However, when using multiple radios per node a channel allocation problem arises, as each radio needs to operate on a specific channel. That channel should be selected so that intra-node interference is avoided and inter-node interference and hidden terminal problems are minimized, while at the same time maintaining connectivity and optimizing performance in terms of channel utilization and throughput.
Channel allocation in multi-radio systems, e.g., in sectorized cellular radios, has traditionally been done using pre-deployment radio planning manually or semi-automatically off-line. This has been feasible as the numbers of nodes have been fairly few, and the cost of professional radio planning is a small percentage of the total cost of deploying the network. However, with WiFi radios operating in unlicensed spectrum and with smaller cell sizes this is no longer true. In such as system the number of nodes will typically be large, and it is not readily knowable before installation how these nodes will interact with the environment in terms of reach, signal bounce and existing interference in the used spectrum.
A feature of IEEE 802.11-type systems is the use of a beacon frame. A typical beacon frame is several tens of bytes in length, with about half of the length being a common frame header and CRC field. As with other frames, the header includes source and destination MAC addresses as well as other information regarding the communications process. The destination address is set to all ones, which is the broadcast MAC address. This forces all other stations on the applicable channel to receive and process each beacon frame. The CRC field provides error detection capability.
The body of the beacon frame is located between the header and the CRC field. Each beacon frame conventionally carries the following information in the frame body.
a) Beacon interval. This represents the amount of time between beacon transmissions. Before a station enters power save mode, the station needs the beacon interval to know when to wake up to receive the beacon (and learn whether there are buffered frames at the AP).b) Timestamp. After receiving a beacon frame, a station uses the timestamp value to update its local clock. This process enables synchronization among all stations that are associated with the same access point.c) Service Set Identifier (SSID). The SSID identifies a specific wireless LAN. Before associating with a particular wireless LAN, a station must have the same SSID as the access point. Access points include the SSID in the beacon frame to enable sniffing functions to identify the SSID and automatically configure the wireless network interface with the proper SSID. In some cases the SSID may not be included for security reasons.d) Supported rates. Each beacon carries information that describes the rates that the particular wireless LAN supports. For example, a beacon may indicate that only certain (1, 2, and 5.5 Mbps) data rates are available. With this information, stations can use performance metrics to decide which access point to associate with.e) Parameter Sets. The beacon includes information about the specific signaling methods (such as frequency hopping spread spectrum, direct sequence spread spectrum, etc.). For example, a beacon would include in the appropriate parameter set the channel number that an IEEE 802.11b access point is using. Likewise, a beacon associated with a frequency hopping network may indicate the frequency hopping pattern and the dwell time at each hopped frequency.f) Capability Information. This field indicates the requirements of stations that wish to join the wireless LAN from where the beacon originated. As one example, the Capabilities Information may indicate that all stations must use wired equivalent privacy (WEP) in order to join the WLAN.g) Traffic Indication Map (TIM). An access point periodically sends the TIM within a beacon to identify which stations using power saving mode have data frames waiting for them in the access point's buffer. The TIM identifies a station by an association ID that the access point assigned to the station during a station association process.
Improvements are needed to the existing beaconing techniques to enhance the operation of a wireless meshed network.